Design of DDSM Modulator without Unwanted Tones with Effective Random Dither

The output of a Digital Delta-Sigma Modulator (DDSM) is always a periodic signal and the input is constant. The frequency synthesizer is commonly used due to its flexibility and convenient frequency adjustment. This paper presents a new method to implement random dither in MASH 1-1-1 modulator. There are two different methods to remove unwanted tones from the MASH modulator output, which are deterministic and random. Deterministic methods include setting the initial conditions of the internal registers, using the first-module quantizer, and the HK-MASH structure. On the other hand, the random method involves applying a random dither signal to the circuit in different ways to eliminate the periodic behavior of the output string. Deterministic methods are not useful for most practical applications. In most practical applications, dither signal is a suitable method. In this article, the disadvantages of different dither methods will be investigated and a new vibration method for MASH sigma-delta modulators for use in fractional frequency synthesizers will be presented.